U.S. patent number 6,801,387 [Application Number 09/834,392] was granted by the patent office on 2004-10-05 for control flow instability to reduce disk flutter and half frequency whirl.
This patent grant is currently assigned to Seagate Technology LLC. Invention is credited to Mohamed M. Rahman.
United States Patent |
6,801,387 |
Rahman |
October 5, 2004 |
Control flow instability to reduce disk flutter and half frequency
whirl
Abstract
To reduce the whirling air vortices which are normally formed at
the disc tip, the outer edge of the disc surface may be gradually
thinned down to a sharp tip. An alternative approach, the disc tip
is gradually reduced in width and rounded at its outer edge. A flow
obstruction may be incorporated in the shroud adjacent the edge of
the disc tip. This obstruction may comprise a small substantially
rectangular insert extending from the inner edge of the housing.
Or, the inner surface of the portion of the housing adjacent the
ends of the disc may incorporate grooves therein. These grooves,
which are roughly herringbone in shape, and would have their center
near either the edge of disc in a single disc environment or
mid-way between the disc in a two disc environment.
Inventors: |
Rahman; Mohamed M. (San Jose,
CA) |
Assignee: |
Seagate Technology LLC (Scotts
Valley, CA)
|
Family
ID: |
33032585 |
Appl.
No.: |
09/834,392 |
Filed: |
April 13, 2001 |
Current U.S.
Class: |
360/99.18;
G9B/33.047 |
Current CPC
Class: |
G11B
33/148 (20130101); G11B 25/043 (20130101) |
Current International
Class: |
G11B
33/14 (20060101); G11B 25/04 (20060101); G11B
033/14 () |
Field of
Search: |
;360/97.02,97.03
;369/280 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Davis; David
Attorney, Agent or Firm: Morrison & Foerster LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims benefit of U.S. provisional patent
application Ser. No. 60/197,221, filed Apr. 14, 2000 and entitled
"Control Flow Instability to Reduce Disk Flutter and Half Frequency
Whirl", which is herein incorporated by reference.
Claims
What is claimed is:
1. In a disc drive storage system comprising at least two rotating
discs cooperating with a spindle motor supported from a base which
supports and rotates the discs, the disc drive further comprising
an actuator assembly for supporting and positioning a transducer
adjacent at least one surface of at least one of the discs, the
disc drive assembly supported within a housing comprising a base, a
cover, and a shroud which is at a radial end of the discs and
spaced from the radial end of the discs, wherein at least one
intermittent obstruction is mounted on an inner surface of the
shroud to intrude into the space between the radial end of the disc
and the inner surface of the shroud to break up the whirling
vortices at the end of at least one of the discs.
2. A disc drive as claimed in claim 1, wherein the edge of at least
one of the discs tapers to a sharp tip.
3. A disc drive as claimed in claim 1 wherein the radial end of at
least one of the discs is curved.
4. A disc drive as claimed in claim 1 wherein the obstruction is
substantially rectangular.
5. A disc drive as claimed in claim 1 wherein the at least one
intermittent obstruction comprises grooves on the inner surface
that channels air away from an end of at least one of the
discs.
6. A disc drive as claimed in claim 5 wherein the grooves are
roughly herringbone shape.
7. A disc drive as claimed in claim 6 wherein the grooves have
their center near a center region between two discs.
8. A disc drive as claimed in claim 1 wherein the at least one
intermittent obstruction comprises a roughened surface region
adjacent an end of at least one of the discs.
9. A disc drive as claimed in claim 8 wherein the roughened surface
region comprises narrow bands adjacent the end of at least one of
the discs.
10. A disc drive as claimed in claim 1, wherein a tip of at least
one of the discs is gradually reduced in width and rounded at an
outer edge of at least one of the discs.
11. A disc drive as claimed in claim 1 wherein the obstruction
comprises an intermittent series of inserts intermittently spaced
around a perphery of at least one of the discs.
12. A disc drive as claimed in claim 1 wherein the radial outer end
of at least one of the discs has an airfoil shape.
Description
FIELD OF THE INVENTION
The present invention generally relates to disc drive apparatus,
and more particularly relates to an improvement in the control of
disc flutter and half frequency whirl to provide enhanced medium to
transducer spacing and stabilization.
BACKGROUND OF THE INVENTION
For successful magnetic recording, particularly at high densities,
such as is currently employed in high density disc drive storage
apparatus, there should be a predictable constant space in between
a record medium and a transducer which is used to access the record
medium for a wide range of operating parameters. Such spacing has a
substantial effect, particularly at high densities on fringing flux
patterns such that the resolution of the sensing and recording on a
record medium is significantly affected. Unfortunately, the
interaction of many parameters, especially with the thin, closely
spaced discs, which are in use today, have a substantial effect on
the predictability and maintainability on such desired constant
spacing. Such parameters include the relative speed between the
record medium and the transducer, and the interior of the surface
areas surrounding the transducer, and disc storage substrate
parameters, such as flexibility and thickness. In addition, given
the very tight spacing margins in present use between a transducer
and the medium, even temperature and humidity can have a
significant effect on variations in medium to transducer
spacing.
Prior attempts to solve this problem have been both complex,
expensive, and space-consuming. For example, in U.S. Pat. No.
3,178,719, a flexible magnetic disc is mounted in close proximity
to a flat air bearing surface of an annular plate referred to as a
Bernoulli plate and is rotated at a relatively fast speed causing
the disc to assume a stable position. A number of magnetic heads
are included in the plate, and a partial vacuum forms around small
areas of the disc around the magnetic heads by a vacuum pump which
is included. Obviously, this is a complex and expensive approach. A
simpler apparatus includes a Bernoulli plate with a groove which is
open to the disk and is readily disposed along the disc; convex
surfaces are located on either side of a head, generating a
pull-down force on the disc in the region near the groove. Once
again, this is an expensive approach requiring considerable
investment in additional parts.
A more recent approach in U.S. Pat. No. 4,578,727 describes a
contact type recording apparatus in which a flat air bearing
surface surrounds an elongate opening to a negative pressure cavity
with the record and playback head arranged in the cavity. The use
of the cavity will help to stabilize the disc surface at least when
it is immediately adjacent to the transducer which is to access the
data on the disc. As with the other approaches, this one consumes
valuable vertical space.
Thus the problem of eliminating flow instability in a high speed
rotating disc continues to need a solution.
SUMMARY OF THE INVENTION
The present invention relates to a device for stabilizing media for
use in a hard disc drive during high speed rotation. More
specifically, the present invention relates to disc media having a
high speed rate of rotation in which means are introduced defined
on the inner surface of the housing for adding stability to the
disc and more specifically to the outer edge of the disc.
Alternatively, to achieve these goals, the design of the disc may
be modified.
In accordance with the present invention, at least in one
embodiment, the outer edge of the disc surface is gradually thinned
down to a sharp tip. In this way, the whirling air vortices which
are normally formed at the disc tip are broken up or diminished. An
alternative approach, the disc tip is gradually reduced in width
and rounded at its outer edge, which also has beneficial results in
terms of breaking up or diminishing the vortices of air which would
otherwise cause instability of the disc.
In a further alternative embodiment of the invention, a flow
obstruction is incorporated in the shroud adjacent the edge of the
disc tip. This obstruction may comprise a small substantially
rectangular insert extending from the inner edge of the housing,
intermittently around the shroud circumference typically adjacent
the edge of the disc tip where one of the vortices would normally
be formed. The presence of this insert would tend to eliminate or
prevent the formation of this air vortex or break the bigger
vortices into smaller and local ones. This insert may further be
used in combination with either a disc of normal thickness or a
disc having a rounded or tapered edge as described above.
In yet another approach or embodiment of the invention, the inner
surface of the housing, and more specifically the portion of the
housing adjacent the ends of the disc which is also referred to as
the shroud, incorporate grooves therein. These grooves which are
roughly herringbone in shape, and would have their center near
either the edge of disc in a single disc environment or mid-way
between the disc in a two disc environment and would tend to
channel the air away from the region where the whirling air vortex
would normally be formed. This approach would also result in
diminishing or eliminating the presence of the whirling air
vortex.
Other features and advantages of this invention will become
apparent to a person of skill in the art who studies the present
invention disclosure given with respect to the following drawings
wherein.
FIG. 1 is an exploded perspective view of a magnetic disc drawing
in which the present invention is useful;
FIG. 2 is a figure illustrating the manner in which more or more
whirling vortexes of air are formed near the tips of discs in a
normal disc drive causing fluttering or instability of the discs;
and
FIGS. 3A and 3B illustrate alternative approaches incorporating
exemplary embodiments of the present invention modifying the disc
design.
FIGS. 3C and 3D are side and end views of an alternative embodiment
modifying the design of the shroud or housing.
FIGS. 3E and 3F illustrate further alternative embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is an exploded perspective view of a magnetic disc drive
storage system in which the modifications to the disc and/or
housing to control flow instability would be useful. Clearly, the
invention herein is not useful solely with the disc drive design
which is shown in FIG. 1, but in almost any disc drive design.
In particular disc drive examples shown here, the storage system
100 includes a housing base 110 having a spindle motor 130 which
carries one or more storage discs 140. An actuator assembly 158
moves transducers 145 across the surface of the discs 140. The
environment of the disc or discs 140 is sealed by seal 120 and
cover 115. In operation, disc 140 rotate at high speed, while
transducers 145 are positioned at any one of a large number of
radially differentiated tracks on the surface of disc 140. This
allows the transducers 145 to read and write magnetically coded
information on the surface of the disc 140 at selected locations.
In order to achieve the design goals for such present day disc
drives as are shown in FIG. 1, it is necessary to be able to
reliably fly the transducer extremely to the surface of the disc on
a long-term basis. To do this requires that a mechanism be provided
to control the flow instability which occurs in a disc drive to
reduce disc flutter and half frequency whirl.
It has been found by analysis of rotating high speed discs that the
finite width of the media 200, such as shown in FIG. 2, results or
is the source of what is called flow instability. Flow analysis in
a disc drive which uses discs 200 of a finite width shows that as
each disc rotates, two counter rotating vortices 202, 204 are
formed adjacent each tip. The size and shape of these vortices 202,
204 also depends on the gap 206 between the disc tip and the shroud
208 (which in fact is the end wall of the housing 115 shown in FIG.
1). Near the periphery 210 of the disc 200, two more larger
vortices 212, 214 are also seen to form adjacent one another
between the discs. These two bigger and stronger vortices interact
with the smaller vortices that form 202, 204 that form at the disc
tip. This interaction process causes unsteadiness in the flow. As a
result, the pressure changes with time adjacent the end of the
disc, causing disc flutter. It has also been concluded by the
inventor that this cyclic interaction has the period of two disc
resolutions. From this it is believed that the interaction process
is responsible for the higher end nonrepeatable runout (NRRO) at
half frequency whirl and some at higher nodes as well. In the
following figures and discussion, a number of solutions to
eliminate the flow instability from the above-mentioned interaction
process are proposed.
Thus referring, for example, to FIG. 3A, the discs 300 are each
shown in this case with a gradually reduced width as indicated by
the dashed lines 302. In a preferred form, the disc would taper
down to a sharp tip 304 at its end. It is immediately evident that
this would substantially reduce if not eliminate the generation of
the counter-rotating vortices 202, 204 which appear in FIG. 2. It
would also reduce the generation of or move the vortices 212, 214
back toward the center of the disc, away from the shroud. In this
way, the disc would be substantially stabilized.
In an alternative approach, rather than tapering the disc to a
sharp tip, it may be simply rounded at its end, as indicated in
FIG. 3B by the dashed lines 310, 312. This would be especially
effective in reducing the size and effectiveness of the rotating
vortices 202, 204. Further, there would not be nearly as much of
the tip width of the disc width which is effective for recording
data lost. However, in both cases, although some region at the end
of the disc may be lost for data recording, in many instances this
region is not recorded in any event. Further, the increased
stability due to diminished disc flutter and half frequency whirl
by the elimination of these whirling vortices would be effective in
allowing for closer packing of the data recording tracks which in
fact are found on the disc surface.
FIG. 3C illustrates a more aggressive approach to breaking up the
whirling vortices at the disc tip. In this approach, an obstruction
402, 404 is mounted on the inner surface of the shroud 208. The
obstruction comprises an intermittent series of inserts 402A, 402B
intermittently spaced around the periphery of the disc which
intrude into the space between the end of the disc 200 and the
inner surface of the shroud adjacent the outer end of each disc, as
shown in FIG. 3D. By intruding into this space, the vortex 202, 204
is broken up or not allowed to form. In this way, even though it is
perhaps going to occur that the overall width of the disc must be
reduced, the effective width of the disc is enhanced by virtue of
the fact that the disc flutter and half frequency whirl is
diminished.
In yet another approach shown in FIG. 3E, grooves 500 which are
preferably of a roughly herringbone shape are imposed or defined on
the inner surface of the shroud 208. These grooves, which have
their center near the center region 508 between the two discs, tend
to channel the air which is otherwise caused to form into the
rotating vortices 202, 204 away from the end points of the discs,
as shown by the arrows 510, 512. Technology for forming such
grooves, which must have a finite width but can be relatively
shallow, exist by virtue of the work done in forming grooves for
hydrodynamic bearings. It would simply be necessary to adapt such
groove forming technology which may be either mechanically done or
found by electrochemical machining, to impose these grooves 507 on
the inner surface of the shroud.
Other approaches to solving the problem of control flow instability
and half frequency whirl identified herein and to which various
solutions are proposed may occur to a person of skill in the art
who studies the above invention disclosure. Another approach could
be by roughening the shroud surface so that flow close to the
shroud is turbulent and forms smaller and weaker vortices.
Roughening the surface would disallow formation of well-defined,
stronger and finite sized vortices such as 212, 214 shown in FIG.
1. Such roughening could be done in narrow bands adjacent the end
of the disc as shown in FIG. 3F. The discs 300 set of vortices 304
as shown. By defining narrow bands 328 of roughened surface region
adjacent each disc end, the vortices can be broken up or
diminished. In another alternative to the approach of FIGS. 3A and
3B, the radial outer end of the disc could have an airfoil shape,
since the disc rotates in a single direction, with the thinnest
part being the trailing edge of the disc. Given the limitations of
disc capacity, disc speed and the expense to be incurred in
adopting any of these solutions, one or more of these solutions may
be preferable or one or more may be used in combination to achieve
the goal of stabilizing the disc and allowing the transducer to fly
closer to the surface of the disc. Therefore, the scope of the
present invention is to be limited only by the following
claims.
* * * * *